Romeo Letor

Sensorless position control of DC actuators for automotive applications

Among automotive actuators, those equipping power windows, seat and mirror positioning require a quite precise position control, either for easy of usage, either for safety reasons. Noticeable cost reductions can be obtained on such kind of actuators by elimination of Hall effect position sensors. This can be accomplished by sensorless estimating the position of the shaft. Unfortunately, because of their limited precision classic sensorless methods based on integration of the armature voltage are not suitable for such specific application. The method proposed in this paper allows one to estimate the position of the rotor shaft by detecting periodical oscillations of the armature current caused by rotor slotting. A key feature of the developed angular position estimation algorithm is that its precision is sufficient to correctly drive a window lift, also performing soft landing and pinch protection, while being suitable to be implemented even on low cost 10 MHz, 8-bit microcontrollers with few kilobites of memory.

Reliability enhancement with the aid of transient infrared thermal analysis of smart Power MOSFETs during short circuit operation

Abstract The usage of novel measurement techniques enhances the capabilities of researchers and power device manufacturers to understand and address reliability problems in novel Smart Power Devices. Along this line of argument, this work describes a method to improve the reliability of the smart Power MOSFET devices by design. The design optimization process involves Silicon layout, interconnections, packaging and protection strategy as well. Accurate thermal transient analyses, made possible by the unique features of a custom infrared radiometric microscope experimental setup which allows dynamic temperature detection with a bandwidth of 1 MHz over the chip area, indicated the way to minimize peak temperature and to verify the effect of the optimization.

Stress analysis and lifetime estimation on power MOSFETs for automotive ABS systems

Stress analysis and lifetime estimation are required in order to guarantee higher and higher levels of reliability of automotive power electronic devices. Stress analysis is oriented to investigate the effects of all the possible physical cause of failures, according to the defined device mission. On the basis of the stress analysis, and of a suitable reliability model a life time prediction can be performed. This is useful to predict the suitability of the device under evaluation to the prescribed mission, as well as to improve the design of new generations of devices. An experimental technique is exploited in this paper to evaluate the stress exerted on planar power MOSFETs designed to equip automotive ABS systems. The technique is based on an accurate experimental analysis of electro-thermal cycles, exploiting a laboratory tool tailored around an infrared microscope. It enables an high resolution dynamic temperature mapping with a large bandwidth. Such a tool makes also possible the evaluation of the effects of charge trapping phenomena occurring on power MOSFETS as result of unavoidable gate overvoltages. According to a reliability model based on the Coffin Manson law, finally it is shown that gate voltage spikes can dramatically reduce the expected life time.

Reliability of planar, Super-Junction and trench low voltage power MOSFETs

A strong demand of even more compact and reliable devices has powered in the last years the development of advanced power MOSFET structures. Among them, the planar STripFET™ has been introduced as an alternative to conventional trench gate MOSFET in low voltage (<60 V) applications. Moreover low voltage Super-Junction devices are also under development. In this paper a conventional trench gate MOSFET is compared in terms of reliability with a STripFET™ and a Super-Junction device. The comparison is accomplished through a reliability model taking advantage from a dynamic analysis of the temperature distribution over the metal source surface in an effort to correlate electric working conditions to thermo-mechanical stresses.

Mixed system integration simplifies the design and the architecture of automotive power actuators

Progress on silicon combined with packaging technologies will be leading the innovation on automotive electronic systems. New packages and advanced chip allow the migration from system on chip to system on package or mixed system integration. Decentralized systems, more and more adopted in automotive architecture, may be implemented without feeling squeezed for cost reductions, performances and design resources. Usage of silicon based drivers for DC motors is imperative for a better management of high current transient across the motor and to achieve safety requirement of the automotive systems. This paper shows the performance and benefits of using devices based on mixed system integration. A specific application-power window motor-is discussed providing the potential architecture of a control unit based on a new multi-island package with optimized chip set and embedded STM proprietary firmware. All technical aspects including thermal and functional are discussed.

An Infrared Thermal Measuring System for Automotive Applications and Reliability Improvement

In the last years the global energy economy hangs in the balance, pushing up the research interest in novel and renewable energy sources and in innovative engines able to improve performances saving the efficiency. This frame requires the development of power electronics subsystems and the continuous increase of working temperatures; hence reliability has become the most critical requirement for any new device design. The temporal evolution of temperature distribution on the surface of a power electronic device undergoing an exerted stress plays a fundamental role in studying and improving reliability. A suitable scanning measuring system has been realized in order to allow the analysis of fast transient states and the localization of “hot-spots” which could be a cause of a premature failure and unreliability of the devices.

Estimation of the shaft position on low-cost DC actuators

Low power DC motors are today largely used as actuators in home automation, office automation, medical equipment and automotive fields. Among automotive applications of DC motors, those regarding windows lifters, seat and mirror adjustment or multi-zone air conditioning, require a quite precise position control, leading to the introduction of suitable sensors. Unfortunately, the extra cost of even a simple Hall effect position sensor may result unacceptable on these systems. In this paper a robust but inexpensive approach is described to sensorless estimate the angular shaft position by counting the periodical pulses of the armature current. Such a pulse counting approach is very simple in principle, as a constant amount of current pulses per round are generated in low power DC motors without any specific intervention. However, the frequency of the current pulses widely varies according to the speed, thus requiring a relatively complex and expensive adjustable bandwidth filter to be correctly detected. The proposed approach suitably solves this problem, leading to the implementation of an accurate position sensorless control system even on ultra-low cost microcontrollers equipping several electrically actuated automotive devices.

Reliability assessment of low-voltage MOSFETs driving inductive loads

Reliability and compactness are two aspects often fighting among themselves when speaking about power electronics, but, indeed, they are the keys for the success of any new circuit or device. Reliability, in particular, is the word of the moment, powering the development of advanced device design techniques having the reliability as a major goal. Endurance tests is the traditional way to evaluate the reliability of power devices. However, they are very time expensive, requiring even months of uninterrupted testing. An interesting alternative is the estimation of the reliability of a device through a suitable model, but, no standard techniques have been developed up to now to accomplish this task. A possible approach is followed in this paper to assess the reliability of Power MOSFETs driving inductive loads, by exploitation of a dynamic analysis of the temperature distribution over the source metal. Coupling such an analysis with a reliability model, carried out from the Coffin-Manson law, the device life time is estimated. Such a procedure is then used to assess the reliability of Power MOS devices tasked to control the brake pump in a modern vehicle. The consistence of the reliability estimation is confirmed by comparison with results of endurance tests. The described approach can be usefully applied to a large set of applications of MOSFETs in the automotive field.

Pulse Counting Sensorless Detection of the Shaft Speed and Position of DC Motor Based Electromechanical Actuators

Some of DC actuators used in home automation, office automation, medical equipment and automotive systems require a position sensor. In low power applications, the introduction of such a transducer remarkably increases the whole system cost, which justifies the development of sensorless position estimation techniques. The well-known AC motor drive sensorless techniques exploiting the fundamental component of the back electromotive force cannot be used on DC motor drives. In addition, the sophisticated approaches based on current or voltage signal injection cannot be used. Therefore, an effective and inexpensive sensorless position estimation technique suitable for DC motors is presented in this paper. This technique exploits the periodic pulses of the armature current caused by commutation. It is based on a simple pulse counting algorithm, suitable for coping with the rather large variability of the pulse frequency and it leads to the realization of a sensorless position control system for low cost, medium performance systems, like those in the field of automotive applications.